Golf balls having foam inner core and themoplastic outer core

ABSTRACT

Multi-piece golf balls containing a dual-core structure are provided. The core structure includes an inner core (center) comprising a foam composition, preferably foamed polyurethane. The outer core layer is preferably formed from a non-foamed thermoplastic composition such as ethylene acid copolymer ionomer. Preferably, the specific gravity (density) of the foam inner core is less than the density of the outer core layer. The ball further includes a cover of at least one layer and may include at least one casing layer. The core structure and resulting ball have relatively good resiliency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a is a divisional of co-pending, co-assigned U.S.patent application Ser. No. 14/844,287 having a filing date of Sep. 3,2015, now allowed, which is divisional of co-assigned U.S. patentapplication Ser. No. 13/913,670 having a filing date of Jun. 10, 2013,now issued as U.S. Pat. No. 9,126,083 with an issue date of Sep. 8,2015, the entire disclosures of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to multi-piece, golf ballshaving a solid core comprising layers made of foam and thermoplasticcompositions. Particularly, the dual-layered core has a foam inner core(center) and surrounding thermoplastic outer core layer. The core layershave different hardness gradients and specific gravity values. The ballfurther includes a cover of at least one layer.

Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. The inner core is made of a natural orsynthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including ethylene acid copolymer ionomers,polyamides, polyesters, polyurethanes, and polyureas.

In recent years, three-piece, four-piece, and even five-piece balls havebecome more popular. New manufacturing technologies, lower materialcosts, and desirable ball playing performance properties havecontributed to these multi-piece balls becoming more popular. Many golfballs used today have multi-layered cores comprising an inner core andat least one surrounding outer core layer. For example, the inner coremay be made of a relatively soft and resilient material, while the outercore may be made of a harder and more rigid material. The “dual-core”sub-assembly is encapsulated by a cover of at least one layer to providea final ball assembly. Different materials can be used to manufacturethe core and cover and impart desirable properties to the final ball.

In general, dual-cores comprising an inner core (or center) and asurrounding outer core layer are known in the industry. For example,Sugimoto, U.S. Pat. No. 6,390,935 discloses a three-piece golf ballcomprising a core having a center and outer shell and a cover disposedabout the core. The specific gravity of the outer shell is greater thanthe specific gravity of the center. The center has a JIS-C hardness (X)at the center point thereof and a JIS-C hardness (Y) at a surfacethereof satisfying the equation: (Y−X)≥8. The core structure (center andouter shell) has a JIS-C hardness (Z) at a surface of 80 or greater. Thecover has a Shore D hardness of less than 60.

Endo, U.S. Pat. No. 6,520,872 discloses a three-piece golf ballcomprising a center, an intermediate layer formed over the center, and acover formed over the intermediate layer. The center is preferably madeof high-cis polybutadiene rubber; and the intermediate and cover layersare preferably made of an ionomer resin such as an ethylene acidcopolymer.

Watanabe, U.S. Pat. No. 7,160,208 discloses a three-piece golf ballcomprising a rubber-based inner core; a rubber-based outer core layer;and a polyurethane elastomer-based cover. The inner core layer has aJIS-C hardness of 50 to 85; the outer core layer has a JIS-C hardness of70 to 90; and the cover has a Shore D hardness of 46 to 55. Also, theinner core has a specific gravity of more than 1.0, and the core outerlayer has a specific gravity equal to or greater than that of that ofthe inner core.

The core sub-structure located inside of the golf ball acts as an engineor spring for the ball. Thus, the composition and construction of thecore is a key factor in determining the resiliency and reboundingperformance of the ball. In general, the rebounding performance of theball is determined by calculating its initial velocity after beingstruck by the face of the golf club and its outgoing velocity aftermaking impact with a hard surface. More particularly, the “Coefficientof Restitution” or “COR” of a golf ball refers to the ratio of a ball'srebound velocity to its initial incoming velocity when the ball is firedout of an air cannon into a rigid vertical plate. The COR for a golfball is written as a decimal value between zero and one. A golf ball mayhave different COR values at different initial velocities. The UnitedStates Golf Association (USGA) sets limits on the initial velocity ofthe ball so one objective of golf ball manufacturers is to maximize CORunder such conditions. Balls with a higher rebound velocity have ahigher COR value. Such golf balls rebound faster, retain more totalenergy when struck with a club, and have longer flight distance asopposed to balls with low COR values. These properties are particularlyimportant for long distance shots. For example, balls having highresiliency and COR values tend to travel a far distance when struck by adriver club from a tee.

The durability, spin rate, and feel of the ball also are importantproperties. In general, the durability of the ball refers to theimpact-resistance of the ball. Balls having low durability appear wornand damaged even when such balls are used only for brief time periods.In some instances, the cover may be cracked or torn. The spin raterefers to the ball's rate of rotation after it is hit by a club. Ballshaving a relatively high spin rate are advantageous for short distanceshots made with irons and wedges. Professional and highly skilledamateur golfers can place a back spin more easily on such balls. Thishelps a player better control the ball and improves shot accuracy andplacement. By placing the right amount of spin on the ball, the playercan get the ball to stop precisely on the green or place a fade on theball during approach shots. On the other hand, recreational players whocannot intentionally control the spin of the ball when hitting it with aclub are less likely to use high spin balls. For such players, the ballcan spin sideways more easily and drift far-off the course, especiallyif it is hooked or sliced. Meanwhile, the “feel” of the ball generallyrefers to the sensation that a player experiences when striking the ballwith the club and it is a difficult property to quantify. Most playersprefer balls having a soft feel, because the player experience a morenatural and comfortable sensation when their club face makes contactwith these balls. Balls having a softer feel are particularly desirablewhen making short shots around the green, because the player senses morewith such balls. The feel of the ball primarily depends upon thehardness and compression of the ball.

Manufacturers of golf balls are constantly looking to differentmaterials for improving the playing performance properties of the ball.Different materials for constructing the core have been considered overthe years. For example, golf balls containing cores made from foamcompositions are generally known in the industry. Puckett and Cadorniga,U.S. Pat. Nos. 4,836,552 and 4,839,116 disclose one-piece, shortdistance golf balls made of a foam composition comprising athermoplastic polymer (ethylene acid copolymer ionomer such as Surlyn®)and filler material (microscopic glass bubbles). The density of thecomposition increases from the center to the surface of the ball. Thus,the ball has relatively dense outer skin and a cellular inner core.According to the '552 and '116 Patents, by providing a short distancegolf ball, which will play approximately 50% of the distance of aconventional golf ball, the land requirements for a golf course can bereduced 67% to 50%.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece golf ball(FIG. 2) containing a high density center (3) made of steel, surroundedby an outer core (4) of low density resilient syntactic foamcomposition, and encapsulated by an ethylene acid copolymer ionomer(Surlyn®) cover (5). The '126 Patent defines the syntactic foam as beinga low density composition consisting of granulated cork or hollowspheres of either phenolic, epoxy, ceramic or glass, dispersed within aresilient elastomer.

Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ballcontaining a core, wherein the core comprising an inner and outerportion, and a cover made of a material such as balata rubber orethylene acid copolymer ionomer. The core is made by foaming, injectinga compressible material, gasses, blowing agents, or gas-containingmicrospheres into polybutadiene or other core material. According to the'889 Patent, polyurethane compositions may be used. The compressiblematerial, for example, gas-containing compressible cells may bedispersed in a limited part of the core so that the portion containingthe compressible material has a specific gravity of greater than 1.00.Alternatively, the compressible material may be dispersed throughout theentire core. In one embodiment, the core comprises an inner and outerportion. In another embodiment, the core comprises inner and outerlayers.

Sullivan and Binette, U.S. Pat. No. 5,833,553 discloses a golf ballhaving core with a coefficient of restitution of at least 0.650 and acover with a thickness of at least 3.6 mm (0.142 inches) and a Shore Dhardness of at least 60. According to the '553 Patent, the combinationof a soft core with a thick, hard cover results in a ball having betterdistance. The '553 Patent discloses that the core may be formed from auniform composition or may be a dual or multi-layer core, and it may befoamed or unfoamed. Polybutadiene rubber, natural rubber, metallocenecatalyzed polyolefins, and polyurethanes are described as being suitablematerials for making the core.

Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf ballcontaining a low specific gravity core and an optional intermediatelayer. This sub-assembly is encased within a high specific gravity coverwith Shore D hardness in the range of about 40 to about 80. The core ispreferably made from a highly neutralized thermoplastic polymer such asethylene acid copolymer which has been foamed. The cover preferably hashigh specific gravity fillers dispersed therein.

Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball comprising: i) apressurized foamed inner center formed from a thermoset material, athermoplastic material, or combinations thereof, a blowing agent and across-linking agent and, ii) an outer core layer formed from a secondthermoset material, a thermoplastic material, or combinations thereof.Additionally, a barrier resin or film can be applied over the outer corelayer to reduce the diffusion of the internal gas and pressure from thenucleus (center and outer core layer). Preferred polymers for thebarrier layer have low permeability such as Saran® film (poly(vinylidene chloride), Barex® resin (acyrlonitrile-co-methyl acrylate),poly (vinyl alcohol), and PET film (polyethylene terephthalate). The'294 Patent does not disclose core layers having different hardnessgradients.

Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654 discloses a golfball having a foamed intermediate layer. Referring to FIG. 1 in the '654Patent, the golf ball includes a core (12), an intermediate layer (14)made of a highly neutralized polymer having a reduced specific gravity(less than 0.95), and a cover (16). According to the '654 Patent, theintermediate layer can be an outer core, a mantle layer, or an innercover. The reduction in specific gravity of the intermediate layer iscaused by foaming the composition of the layer and this reduction can beas high as 30%. The '654 Patent discloses that other foamed compositionssuch as foamed polyurethanes and polyureas may be used to form theintermediate layer.

Tutmark, U.S. Pat. No. 8,272,971 is directed to golf balls containing anelement that reduces the distance of the ball's flight path. In oneembodiment, the ball includes a core and cover. A cavity is formedbetween core and cover and this may be filled by a foamed polyurethane“middle layer” in order to dampen the ball's flight properties. The foamof the middle layer is relatively light in weight; and the core isrelatively heavy and dense. According to the '971 Patent, when a golferstrikes the ball with a club, the foam in the middle layer actuates andcompresses, thereby absorbing much of the impact from the impact of theball.

Although some foam core constructions for gold balls have beenconsidered over the years, there are drawbacks with using such foammaterials. For example, one disadvantage with golf balls having a foamcore is the ball tends to have low resiliency. That is, the velocity ofthe ball tends to be low after being hit by a club and the ballgenerally travels short distances. Golf balls having foam inner coresare often referred to as reduced-distance balls. There is a need for newballs having a foam core with improved resiliency that will allowplayers to generate higher initial ball speed. This will allow playersto make longer distance shots. The present invention provides new foamcore constructions having improved resiliency as well as otheradvantageous properties, features, and benefits. The invention alsoencompasses golf balls containing the improved core constructions.

SUMMARY OF THE INVENTION

The present invention provides a multi-piece golf ball comprising asolid core having two layers and a cover having at least one layer. Inone version, the dual-layered core includes: i) an inner core (center)comprising a foamed composition, wherein the inner core has a diameterin the range of about 0.100 to about 1.100 inches and a specific gravity(SG_(inner)); and ii) an outer core layer comprising a thermoplasticmaterial, wherein the outer core layer is disposed about the inner coreand has a thickness in the range of about 0.100 to about 0.750 inchesand a specific gravity (SG_(outer)). Preferably, the SG_(outer) isgreater than the SG_(inner).

Preferably, the inner core comprises a foam polyurethane compositionprepared from a mixture comprising polyisocyanate, polyol, and curingagent compounds, and blowing agent. Aromatic and aliphaticpolyisocyanates may be used. The foamed polyurethane composition may beprepared by using water as a blowing agent. The water is added to themixture in a sufficient amount to cause the mixture to foam. Surfactantsand catalysts, such as zinc and tin-based catalysts, may be included inthe mixture.

Thermoplastic materials are used to form the outer core layer in thepresent invention. Preferably, the thermoplastic materials arenon-foamed. Thus, the dual-core includes a foam inner core (center) anda surrounding non-foamed thermoplastic core layer. For example,thermoplastic ethylene acid copolymer ionomer compositions may be usedto form the outer core. In one example, the outer core layer has athickness in the range of about 0.250 to about 0.750 inches and aspecific gravity in the range of about 0.60 to about 2.90 g/cc.

The core layers may have different hardness gradients. For example, eachcore layer may have a positive, zero, or negative hardness gradient. Ina first embodiment, the inner core has a positive hardness gradient; andthe outer core layer has a positive hardness gradient. In a secondembodiment, the inner core has a positive hardness gradient, and theouter core layer has zero or negative hardness gradient. In yet anotherversion, the inner core has a zero or negative hardness gradient; andthe outer core layer has a positive hardness gradient. In anotheralternative version, both the inner and outer core layers have zero ornegative hardness gradients.

More particularly, in one preferred embodiment, the inner core has apositive hardness gradient, wherein the hardness of the geometric center(H_(inner core center)) is in the range of about 30 to about 78 Shore C;and the hardness of the surface of the inner core(H_(inner core surface)) is in the range of about 46 to about 95 ShoreC. In another preferred embodiment, the hardness of the geometric center(H_(inner core center)) is in the range of about 10 to about 50 Shore C;and the hardness of the surface of the inner core(H_(inner core surface)) is in the range of about 13 to about 60 ShoreC. The inner core layer also may have different thicknesses and specificgravities. For example, the inner core has a diameter in the range ofabout 0.100 to about 0.900 inches, for example 0.400 to 0.800 inches;and a specific gravity in the range of about 0.25 to about 1.25 g/cc,for example 0.30 to 0.95 g/cc.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a spherical inner core made of a foamedcomposition in accordance with the present invention;

FIG. 2 is a perspective view of one embodiment of upper and lower moldcavities used to make the dual-layered cores of the present invention;

FIG. 3 is a cross-sectional view of a three-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 4 is a cross-sectional view of a four-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 5A is a graph showing the hardness of a dual-layered core having adiameter of 0.5 inches (foam center and thermoplastic outer layer) atdifferent points in the core structure per a first example of thisinvention;

FIG. 5B is a graph showing the hardness of a dual-layered core having adiameter of 0.5 inches (foam center and thermoplastic outer layer) atdifferent points in the core structure per a second example of thisinvention;

FIG. 5C is a graph showing the hardness of a dual-layered core having adiameter of 0.5 inches (foam center and thermoplastic outer layer) atdifferent points in the core structure per a third example of thisinvention; and

FIG. 5D is a graph showing the hardness of a dual-layered core having adiameter of 0.75 inches (foam center and thermoplastic outer layer) atdifferent points in the core structure per a fourth example of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three piece, four-piece,and five-piece constructions with single or multi-layered covermaterials may be made. Representative illustrations of such golf ballconstructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a three-piece golf ballcontaining a dual-layered core and single-layered cover is made. Thedual-core includes an inner core (center) and surrounding outer corelayer. In another version, a four-piece golf ball containing a dual-coreand dual-cover (inner cover and outer cover layers) is made. In yetanother construction, a four-piece or five-piece golf ball containing adual-core; casing layer(s); and cover layer(s) may be made. As usedherein, the term, “casing layer” means a layer of the ball disposedbetween the multi-layered core sub-assembly and cover. The casing layeralso may be referred to as a mantle or intermediate layer. The diameterand thickness of the different layers along with properties such ashardness and compression may vary depending upon the construction anddesired playing performance properties of the golf ball.

Inner Core—Foam Composition

In general, foam compositions are made by forming gas bubbles in apolymer mixture using a foaming (blowing) agent. As the bubbles form,the mixture expands and forms a foam composition that can be molded intoan end-use product having either an open or closed cellular structure.Flexible foams generally have an open cell structure, where the cellswalls are incomplete and contain small holes through which liquid andair can permeate. Such flexible foams are used for automobile seats,cushioning, mattresses, and the like. Rigid foams generally have aclosed cell structure, where the cell walls are continuous and complete,and are used for used for automobile panels and parts, buildinginsulation and the like.

In the present invention, the inner core (center) comprises alightweight foam thermoplastic or thermoset polymer composition that mayrange from a relatively rigid foam to a very flexible foam. Referring toFIG. 1, a foamed inner core (4) having a geometric center (6) and outerskin (8) may be prepared in accordance with this invention.

A wide variety of thermoplastic and thermoset materials may be used informing the foam composition of this invention including, for example,polyurethanes; polyureas; copolymers, blends and hybrids of polyurethaneand polyurea; olefin-based copolymer ionomer resins (for example,Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000, commerciallyavailable from DuPont; Iotek® ionomers, commercially available fromExxonMobil Chemical Company; Amplify® IO ionomers of ethylene acrylicacid copolymers, commercially available from Dow Chemical Company; andClarix® ionomer resins, commercially available from A. Schulman Inc.);polyethylene, including, for example, low density polyethylene, linearlow density polyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, commercially available from ArkemaInc; cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinggood playing performance properties as discussed further below. By theterm, “hybrids of polyurethane and polyurea,” it is meant to includecopolymers and blends thereof.

Basically, polyurethane compositions contain urethane linkages formed bythe reaction of a multi-functional isocyanate containing two or more NCOgroups with a polyol having two or more hydroxyl groups (OH—OH)sometimes in the presence of a catalyst and other additives. Generally,polyurethanes can be produced in a single-step reaction (one-shot) or ina two-step reaction via a prepolymer or quasi-prepolymer. In theone-shot method, all of the components are combined at once, that is,all of the raw ingredients are added to a reaction vessel, and thereaction is allowed to take place. In the prepolymer method, an excessof polyisocyanate is first reacted with some amount of a polyol to formthe prepolymer which contains reactive NCO groups. This prepolymer isthen reacted again with a chain extender or curing agent polyol to formthe final polyurethane. Polyurea compositions, which are distinct fromthe above-described polyurethanes, also can be formed. In general,polyurea compositions contain urea linkages formed by reacting anisocyanate group (—N═C═O) with an amine group (NH or NH₂). Polyureas canbe produced in similar fashion to polyurethanes by either a one shot orprepolymer method. In forming a polyurea polymer, the polyol would besubstituted with a suitable polyamine. Hybrid compositions containingurethane and urea linkages also may be produced. For example, whenpolyurethane prepolymer is reacted with amine-terminated curing agentsduring the chain-extending step, any excess isocyanate groups in theprepolymer will react with the amine groups in the curing agent. Theresulting polyurethane-urea composition contains urethane and urealinkages and may be referred to as a hybrid. In another example, ahybrid composition may be produced when a polyurea prepolymer is reactedwith a hydroxyl-terminated curing agent. A wide variety of isocyanates,polyols, polyamines, and curing agents can be used to form thepolyurethane and polyurea compositions as discussed further below.

To prepare the foamed polyurethane, polyurea, or other polymercomposition, a foaming agent is introduced into the polymer formulation.In general, there are two types of foaming agents: physical foamingagents and chemical foaming agents.

Physical Foaming Agents.

These foaming agents typically are gasses that are introduced under highpressure directly into the polymer composition. Chlorofluorocarbons(CFCs) and partially halogenated chlorofluorocarbons are effective, butthese compounds are banned in many countries because of theirenvironmental side effects. Alternatively, aliphatic and cyclichydrocarbon gasses such as isobutene and pentane may be used. Inertgasses, such as carbon dioxide and nitrogen, also are suitable.

Chemical Foaming Agents.

These foaming agents typically are in the form of powder, pellets, orliquids and they are added to the composition, where they decompose orreact during heating and generate gaseous by-products (for example,nitrogen or carbon dioxide). The gas is dispersed and trapped throughoutthe composition and foams it.

Preferably, a chemical foaming agent is used to prepare the foamcompositions of this invention. Chemical blowing agents may beinorganic, such as ammonium carbonate and carbonates of alkalai metals,or may be organic, such as azo and diazo compounds, such asnitrogen-based azo compounds. Suitable azo compounds include, but arenot limited to, 2,2′-azobis(2-cyanobutane),2,2′-azobis(methylbutyronitrile), azodicarbonamide, p,p′-oxybis(benzenesulfonyl hydrazide), p-toluene sulfonyl semicarbazide, p-toluenesulfonyl hydrazide. Other foaming agents include any of the Celogens®sold by Crompton Chemical Corporation, and nitroso compounds,sulfonylhydrazides, azides of organic acids and their analogs,triazines, tri- and tetrazole derivatives, sulfonyl semicarbazides, ureaderivatives, guanidine derivatives, and esters such as alkoxyboroxines.Also, foaming agents that liberate gasses as a result of chemicalinteraction between components such as mixtures of acids and metals,mixtures of organic acids and inorganic carbonates, mixtures of nitrilesand ammonium salts, and the hydrolytic decomposition of urea may beused. Water is a preferred foaming agent. When added to the polyurethaneformulation, water will react with the isocyanate groups and formcarbamic acid intermediates. The carbamic acids readily decarboxylate toform an amine and carbon dioxide. The newly formed amine can thenfurther react with other isocyanate groups to form urea linkages and thecarbon dioxide forms the bubbles to produce the foam.

During the decomposition reaction of certain chemical foaming agents,more heat and energy is released than is needed for the reaction. Oncethe decomposition has started, it continues for a relatively long timeperiod. If these foaming agents are used, longer cooling periods aregenerally required. Hydrazide and azo-based compounds often are used asexothermic foaming agents. On the other hand, endothermic foaming agentsneed energy for decomposition. Thus, the release of the gasses quicklystops after the supply of heat to the composition has been terminated.If the composition is produced using these foaming agents, shortercooling periods are needed. Bicarbonate and citric acid-based foamingagents can be used as exothermic foaming agents.

Other suitable foaming agents include expandable gas-containingmicrospheres. Exemplary microspheres consist of an acrylonitrile polymershell encapsulating a volatile gas, such as isopentane gas. This gas iscontained within the sphere as a blowing agent. In their unexpandedstate, the diameter of these hollow spheres range from 10 to 17 μm andhave a true density of 1000 to 1300 kg/m³. When heated, the gas insidethe shell increases its pressure and the thermoplastic shell softens,resulting in a dramatic increase of the volume of the microspheres.Fully expanded, the volume of the microspheres will increase more than40 times (typical diameter values would be an increase from 10 to 40μm), resulting in a true density below 30 kg/m³ (0.25 lbs/gallon).Typical expansion temperatures range from 80-190° C. (176-374° F.). Suchexpandable microspheres are commercially available as Expancel® fromExpancel of Sweden or Akzo Nobel.

As an alternative to chemical and physical foaming agents or in additionto such foaming agents, as described above, other types of fillers thatlower the specific gravity of the composition can be used in accordancewith this invention. For example, polymeric, ceramic, and glass unfilledmicrospheres having a density of 0.1 to 1.0 g/cc and an average particlesize of 10 to 250 microns can be used to help lower specific gravity ofthe composition and achieve the desired density and physical properties.

Additionally, BASF polyurethane materials sold under the trade nameCellasto® and Elastocell®, microcellular polyurethanes, Elastopor® Hthat is a closed-cell polyurethane rigid foam, Elastoflex® W flexiblefoam systems, Elastoflex®E semiflexible foam systems, Elastofoam®flexible integrally-skinning systems, Elastolit®D/K/R integral rigidfoams, Elastopan®S, Elastollan® thermoplastic polyurethane elastomers(TPUs), and the like may be used in accordance with the presentinvention. Bayer also produces a variety of materials sold as Texin®TPUs, Baytec® and Vulkollan® elastomers, Baymer® rigid foams, Baydur®integral skinning foams, Bayfit® flexible foams available as castable,RIM grades, sprayable, and the like that may be used. Additional foammaterials that may be used herein include polyisocyanurate foams and avariety of “thermoplastic” foams, which may be cross-linked to varyingextents using free-radical (for example, peroxide) or radiationcross-linking (for example, UV, IR, Gamma, EB irradiation). Also, foamsmay be prepared from polybutadiene, polystyrene, polyolefin (includingmetallocene and other single site catalyzed polymers), ethylene vinylacetate (EVA), acrylate copolymers, such as EMA, EBA, Nucrel®-type acidco and terpolymers, ethylene propylene rubber (such as EPR, EPDM, andany ethylene copolymers), styrene-butadiene, and SEBS (any Kraton-type),PVC, PVDC, CPE (chlorinated polyethylene). Epoxy foams,urea-formaldehyde foams, latex foams and sponge, silicone foams,fluoropolymer foams and syntactic foams (hollow sphere filled) also maybe used.

In addition to the polymer and foaming agent, the foam composition alsomay include other ingredients such as, for example, cross-linkingagents, chain extenders, surfactants, dyes and pigments, coloringagents, fluorescent agents, adsorbents, stabilizers, softening agents,impact modifiers, antioxidants, antiozonants, and the like. Theformulations used to prepare the polyurethane foam compositions of thisinvention preferably contain a polyol, polyisocyanate, water, an amineor hydroxyl curing agent, surfactant, and a catalyst as describedfurther below.

Properties of Polyurethane Foams

The polyurethane foam compositions of this invention have numerouschemical and physical properties making them suitable for coreassemblies in golf balls. For example, there are properties relating tothe reaction of the isocyanate and polyol components and blowing agent,particularly “cream time,” “gel time,” “rise time,” “tack-free time,”and “free-rise density.” In general, cream time refers to the timeperiod from the point of mixing the raw ingredients together to thepoint where the mixture turns cloudy in appearance or changes color andbegins to rise from its initial stable state. Normally, the cream timeof the foam compositions of this invention is within the range of about20 to about 240 seconds. In general, gel time refers to the time periodfrom the point of mixing the raw ingredients together to the point wherethe expanded foam starts polymerizing/gelling. Rise time generallyrefers to the time period from the point of mixing the raw ingredientstogether to the point where the reacted foam has reached its largestvolume or maximum height. The rise time of the foam compositions of thisinvention typically is in the range of about 60 to about 360 seconds.Tack-free time generally refers to the time it takes for the reactedfoam to lose its tackiness, and the foam compositions of this inventionnormally have a tack-free time of about 60 to about 3600 seconds.Free-rise density refers to the density of the resulting foam when it isallowed to rise unrestricted without a cover or top being placed on themold.

The density of the foam is an important property and is defines as theweight per unit volume (typically, kg/m³ or lb/ft³ or g/cm³) and can bemeasured per ASTM D-1622. The hardness, stiffness, and load-bearingcapacity of the foam are independent of the foam's density, althoughfoams having a high density typically have high hardness and stiffness.Normally, foams having higher densities have higher compressionstrength. Surprisingly, the foam compositions used to produce the innercore of the golf balls per this invention have a relatively low density;however, the foams are not necessarily soft and flexible, rather, theymay be relatively firm, rigid, or semi-rigid depending upon the desiredgolf ball properties. Tensile strength, tear-resistance, and elongationgenerally refer to the foam's ability to resist breaking or tearing, andthese properties can be measured per ASTM D-1623. The durability offoams is important, because introducing fillers and other additives intothe foam composition can increase the tendency of the foam to break ortear apart. In general, the tensile strength of the foam compositions ofthis invention is in the range of about 20 to about 1000 psi (parallelto the foam rise) and about 50 to about 1000 psi (perpendicular to thefoam rise) as measured per ASTM D-1623 at 23° C. and 50% relativehumidity (RH). Meanwhile, the flex modulus of the foams of thisinvention is generally in the range of about 5 to about 45 kPa asmeasured per ASTM D-790, and the foams generally have a compressivemodulus of 200 to 50,000 psi.

In another test, compression strength is measured on an Instron machineaccording to ASTM D-1621. The foam is cut into blocks and thecompression strength is measured as the force required to compress theblock by 10%. In general, the compressive strength of the foamcompositions of this invention is in the range of about 100 to about1800 psi (parallel and perpendicular to the foam rise) as measured perASTM D-1621 at 23° C. and 50% relative humidity (RH). The test isconducted perpendicular to the rise of the foam or parallel to the riseof the foam. The Percentage (%) of Compression Set also can be used.This is a measure of the permanent deformation of a foam sample after ithas been compressed between two metal plates under controlled time andtemperature condition (standard—22 hours at 70° C. (158° F.)). The foamis compressed to a thickness given as a percentage of its originalthickness that remained “set.” Preferably, the Compression Set of thefoam is less than ten percent (10%), that is, the foam recovers to apoint of 90% or greater of its original thickness.

Methods of Preparing the Foam Composition

The foam compositions of this invention may be prepared using differentmethods. In one preferred embodiment, the method involves preparing acastable composition comprising a reactive mixture of a polyisocyanate,polyol, water, curing agent, surfactant, and catalyst. A motorized mixercan be used to mix the starting ingredients together and form a reactiveliquid mixture. Alternatively, the ingredients can be manually mixedtogether. An exothermic reaction occurs when the ingredients are mixedtogether and this continues as the reactive mixture is dispensed intothe mold cavities (otherwise referred to as half-molds or mold cups).The mold cavities may be referred to as first and second, or upper andlower, mold cavities. The mold cavities preferably are made of metalsuch as, for example, brass or silicon bronze.

Referring to FIG. 2, the mold cavities are generally indicated at (9)and (10). The lower and upper mold cavities (9, 10) are placed in lowerand upper mold frame plates (11, 12). The frame plates (11, 12) containguide pins and complementary alignment holes (not shown in drawing). Theguide pins are inserted into the alignment holes to secure the lowerplate (11) to the upper plate (12). The lower and upper mold cavities(9, 10) are mated together as the frame plates (11, 12) are fastened.When the lower and upper mold cavities (9, 10) are joined together, theydefine an interior spherical cavity that houses the spherical core. Theupper mold contains a vent or hole (14) to allow for the expanding foamto fill the cavities uniformly. A secondary overflow chamber (16), whichis located above the vent (14), can be used to adjust the amount of foamoverflow and thus adjust the density of the core structure being moldedin the cavities. As the lower and upper mold cavities (9, 10) are matedtogether and sufficient heat and pressure is applied, the foamedcomposition cures and solidifies to form a relatively rigid andlightweight spherical core. The resulting cores are cooled and thenremoved from the mold.

Hardness of the Inner Core

As shown in FIG. 1, a foamed inner core (4) having a geometric center(6) and outer skin (8) may be prepared per the molding method discussedabove. The outer skin (8) is generally a non-foamed region that formsthe outer surface of the core structure. The resulting inner corepreferably has a diameter within a range of about 0.100 to about 1.100inches. For example, the inner core may have a diameter within a rangeof about 0.100 to about 0.500 inches. In another example, the inner coremay have a diameter within a range of about 0.250 to about 1.000 inches.In yet another example, the inner core may have a diameter within arange of about 0.400 to about 0.800 inches. More particularly, the innercore preferably has a diameter size with a lower limit of about 0.10 or0.12 or 0.15 or 0.25 or 0.30 or 0.35 or 0.45 or 0.55 inches and an upperlimit of about 0.60 or 0.65 or 0.70 or 0.80 or 0.90 or 1.00 or 1.10inches. The outer skin (8) of the inner core is relatively thinpreferably having a thickness of less than about 0.020 inches and morepreferably less than 0.010 inches. In one preferred embodiment, thefoamed core has a “positive” hardness gradient (that is, the outer skinof the inner core is harder than its geometric center.)

For example, the geometric center hardness of the inner core(H_(inner core center)), as measured in Shore C units, is about 10 ShoreC or greater and preferably has a lower limit of about 10 or 16 or 20 or25 or 30 or 32 or 34 or 36 or 40 Shore C and an upper limit of about 42or 44 or 48 or 50 or 52 or 56 or 60 or 62 or 65 or 68 or 70 or 74 or 78or 80 Shore C. In one preferred version, the geometric center hardnessof the inner core (H_(inner core center)) is about 60 Shore C. When aflexible, relatively soft foam is used, the foam may have a Shore Ahardness of about 10 or greater, and preferably has a lower limit of 15,20, 25, 30, or 35 Shore A and an upper limit of about 60, 65, 70, 80,85, or 90 Shore A. In one preferred embodiment, the geometric centerhardness of the inner core is about 55 Shore A. TheH_(inner core center), as measured in Shore D units, is about 15 Shore Dor greater and more preferably within a range having a lower limit ofabout 15 or 18 or 20 or 22 or 25 or 28 or 30 or 32 or 36 or 40 or 44Shore D and an upper limit of about 45 or 48 or 50 or 52 or 55 or 58 or60 or 62 or 64 or 66 or 70 or 72 or 74 or 78 or 80 or 82 or 84 or 88 or90 Shore D. Meanwhile, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C, is about 20 Shore C orgreater and preferably has a lower limit of about 13 or 17 or 20 or 22or 24 or 28 or 30 or 32 or 35 or 36 or 40 or 42 or 44 or 46 or 48 or 50Shore C and an upper limit of about 52 or 55 or 58 or 60 or 62 or 64 or66 or 70 or 74 or 78 or 80 or 86 or 88 or 90 or 92 or 95 Shore C. Theouter surface hardness of the inner core (H_(inner core surface)), asmeasured in Shore D units, preferably has a lower limit of about 25 or28 or 30 or 32 or 36 or 40 or 44 Shore D and an upper limit of about 45or 48 or 50 or 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 74 or 78or 80 or 82 or 84 or 88 or 90 or 94 or 96 Shore D. In one preferredembodiment, the H_(inner core center) is in the range of about 10 ShoreC to about 50 Shore C, and the H_(inner core surface) is in the range ofabout 13 Shore C to about 60 Shore C.

Density of the Inner Core

The foamed inner core preferably has a specific gravity of about 0.25 toabout 1.25 g/cc. That is, the density of the inner core (as measured atany point of the inner core structure) is preferably within the range ofabout 0.25 to about 1.25 g/cc. By the term, “specific gravity of theinner core” (“SG_(inner)”), it is generally meant the specific gravityof the inner core as measured at any point of the inner core structure.It should be understood, however, that the specific gravity values, astaken at different points of the inner core structure, may vary. Forexample, the foamed inner core may have a “positive” density gradient(that is, the outer surface (skin) of the inner core may have a densitygreater than the geometric center of the inner core.) In one preferredversion, the specific gravity of the geometric center of the inner core(SG_(center of inner core)) is less than 1.00 g/cc and more preferably0.90 g/cc or less. More particularly, in one version, the(SG_(center of inner core)) is in the range of about 0.10 to about 0.90g/cc. For example, the (SG_(center of inner core)) may be within a rangehaving a lower limit of about 0.10 or 0.15 of 0.20 or 0.24 or 0.25 or0.30 or 0.35 or 0.37 or 0.40 or 0.42 or 0.45 or 0.47 or 0.50 and anupper limit of about 0.60 or 0.65 or 0.70 or 0.74 or 0.78 or 0.80, or0.82 or 0.84 or 0.85 or 0.88 or 0.90 or 0.95 g/cc. Meanwhile, thespecific gravity of the outer surface (skin) of the inner core(SG_(skin of inner core)), in one preferred version, is greater thanabout 0.90 g/cc and more preferably greater than 1.00 g/cc. For example,the (SG_(skin of inner core)) may fall within the range of about 0.90 toabout 2.00. More particularly, in one version, the(SG_(skin of inner core)) may have a specific gravity with a lower limitof about 0.90 or 0.92 or 0.95 or 0.98 or 1.00 or 1.02 or 1.06 or 1.10 or1.12 or 1.15 or 1.18 and an upper limit of about 1.20 or 1.24 or 1.30 or1.32 or 1.35 or 1.38 or 1.40 or 1.44 or 1.50 or 1.60 or 1.65 or 1.70 or1.76 or 1.80 or 1.90 or 1.92 or 2.00. In other instances, the outer skinmay have a specific gravity of less than 0.90 g/cc. For example, thespecific gravity of the outer skin (SG_(skin of inner core)) may beabout 0.75 or 0.80 or 0.82 or 0.85 or 0.88 g/cc. In such instances,wherein both the (SG_(center of inner core)) and(SG_(skin of inner core)) are less than 0.90 g/cc, it is still preferredthat the (SG_(center of inner core)) is less than the(SG_(skin of inner core)).

Polyisocyanates and Polyols for Making the Polyurethane Foams

As discussed above, in one preferred embodiment, a foamed polyurethanecomposition is used to form the inner core. In general, the polyurethanecompositions contain urethane linkages formed by reacting an isocyanategroup (—N═C═O) with a hydroxyl group (OH). The polyurethanes areproduced by the reaction of multi-functional isocyanates containing twoor more isocyanate groups with a polyol having two or more hydroxylgroups. The formulation may also contain a catalyst, surfactant, andother additives.

In particular, the foam inner core of this invention may be preparedfrom a composition comprising an aromatic polyurethane, which ispreferably formed by reacting an aromatic diisocyanate with a polyol.Suitable aromatic diisocyanates that may be used in accordance with thisinvention include, for example, toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and homopolymersand copolymers and blends thereof. The aromatic isocyanates are able toreact with the hydroxyl or amine compounds and form a durable and toughpolymer having a high melting point. The resulting polyurethanegenerally has good mechanical strength and tear-resistance.

Alternatively, the foamed composition of the inner core may be preparedfrom a composition comprising aliphatic polyurethane, which ispreferably formed by reacting an aliphatic diisocyanate with a polyol.Suitable aliphatic diisocyanates that may be used in accordance withthis invention include, for example, isophorone diisocyanate (IPDI),1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDI”), meta-tetramethylxylyene diisocyanate (TMXDI),trans-cyclohexane diisocyanate (CHDI),1,3-bis(isocyanatomethyl)cyclohexane;1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and copolymersand blends thereof. The resulting polyurethane generally has good lightand thermal stability. Preferred polyfunctional isocyanates include4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylene diphenyldiisocyanate (MDI), and polymeric MDI having a functionality in therange of 2.0 to 3.5 and more preferably 2.2 to 2.5.

Any suitable polyol may be used to react with the polyisocyanate inaccordance with this invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

As discussed further below, chain extenders (curing agents) are added tothe mixture to build-up the molecular weight of the polyurethanepolymer. In general, hydroxyl-terminated curing agents, amine-terminatedcuring agents, and mixtures thereof are used.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds. Suitable catalysts include, but are notlimited to, bismuth catalyst; zinc octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, tributylamine, 1,4-diaza(2,2,2)bicyclooctane,tetramethylbutane diamine, bis[2-dimethylaminoethyl]ether,N,N-dimethylaminopropylamine, N,N-dimethylcyclohexylamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine, diethanolamine,dimethylethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine,N-ethylmorpholine, 3-dimethylamino-N,N-dimethylpropionamide, andN,N′,N″-dimethylaminopropylhexahydrotriazine; organic acids such asoleic acid and acetic acid; delayed catalysts; and mixtures thereof.Zirconium-based catalysts such as, for example, bis(2-dimethylaminoethyl) ether; mixtures of zinc complexes and amine compounds suchas KKAT™ XK 614, available from King Industries; and amine catalystssuch as Niax™ A-2 and A-33, available from Momentive SpecialtyChemicals, Inc. are particularly preferred. The catalyst is preferablyadded in an amount sufficient to catalyze the reaction of the componentsin the reactive mixture. In one embodiment, the catalyst is present inan amount from about 0.001 percent to about 1 percent, and preferably0.1 to 0.5 percent, by weight of the composition.

In one preferred embodiment, as described above, water is used as thefoaming agent—the water reacts with the polyisocyanate compound(s) andforms carbon dioxide gas which induces foaming of the mixture. Thereaction rate of the water and polyisocyanate compounds affects howquickly the foam is formed as measured per reaction profile propertiessuch as cream time, gel time, and rise time of the foam.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof. Di, tri, and tetra-functional polycaprolactone diols such as,2-oxepanone polymer initiated with 1,4-butanediol,2-ethyl-2-(hydroxymethyl)-1,3-propanediol, or2,2-bis(hydroxymethyl)-1,3-propanediol such, may be used.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-) toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benzeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3′-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”),4,4′-bis(sec-butylamino)-diphenylmethane,N,N′-dialkylamino-diphenylmethane,trimethyleneglycol-di(p-aminobenzoate),polyethyleneglycol-di(p-aminobenzoate),polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines such asethylene diamine, 1,3-propylene diamine, 2-methyl-pentamethylenediamine, hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, imino-bis(propylamine), imido-bis(propylamine),methylimino-bis(propylamine) (i.e.,N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane (i.e.,3,3′-[1,4-butanediylbis-(oxy)bis]-1-propanamine),diethyleneglycol-bis(propylamine) (i.e.,diethyleneglycol-di(aminopropyl)ether),4,7,10-trioxatridecane-1,13-diamine, 1-methyl-2,6-diamino-cyclohexane,1,4-diamino-cyclohexane, poly(oxyethylene-oxypropylene) diamines, 1,3-or 1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane,polyoxypropylene diamines,3,3′-diethyl-5,5′-dichloro-4,4′-diamino-dicyclohexylmethane,polytetramethylene ether diamines,3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaminocyclohexane)),3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane,(ethylene oxide)-capped polyoxypropylene ether diamines,2,2′,3,3′-tetrachloro-4,4′-diamino-dicyclohexylmethane,4,4′-bis(sec-butylamino)-dicyclohexylmethane; triamines such asdiethylene triamine, dipropylene triamine, (propylene oxide)-basedtriamines (i.e., polyoxypropylene triamines),N-(2-aminoethyl)-1,3-propylenediamine (i.e., N₃-amine), glycerin-basedtriamines, (all saturated); tetramines such asN,N′-bis(3-aminopropyl)ethylene diamine (i.e., N₄-amine) (bothsaturated), triethylene tetramine; and other polyamines such astetraethylene pentamine (also saturated). One suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When a hydroxyl-terminated curing agent is used, the resultingpolyurethane composition contains urethane linkages. On the other hand,when an amine-terminated curing agent is used, any excess isocyanategroups will react with the amine groups in the curing agent. Theresulting polyurethane composition contains urethane and urea linkagesand may be referred to as a polyurethane/urea hybrid.

Outer Core Layer—Thermoplastic Compositions

As discussed above, the inner core is made preferably from a foamedcomposition. Meanwhile, the outer core layer, which surrounds the innercore, is formed preferably from a non-foamed thermoplastic composition.

More particularly, the outer core layer is formed preferably from anionomer composition containing acid groups that are at leastpartially-neutralized. Suitable ionomer compositions includepartially-neutralized ionomers and highly-neutralized ionomers (HNPs),including ionomers formed from blends of two or morepartially-neutralized ionomers, blends of two or more highly-neutralizedionomers, and blends of one or more partially-neutralized ionomers withone or more highly-neutralized ionomers. For purposes of the presentdisclosure, “HNP” refers to an acid copolymer after at least 70% of allacid groups present in the composition are neutralized. Preferredionomers are salts of O/X- and O/X/Y-type acid copolymers, wherein O isan α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid,and Y is a softening monomer. O is preferably selected from ethylene andpropylene. X is preferably selected from methacrylic acid, acrylic acid,ethacrylic acid, crotonic acid, and itaconic acid. Methacrylic acid andacrylic acid are particularly preferred. Y is preferably selected from(meth) acrylate and alkyl (meth) acrylates wherein the alkyl groups havefrom 1 to 8 carbon atoms, including, but not limited to, n-butyl (meth)acrylate, isobutyl (meth) acrylate, methyl (meth) acrylate, and ethyl(meth) acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/isobutyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α,β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

The α-olefin is typically present in the O/X or O/X/Y-type copolymer inan amount of 15 wt. % or greater, or 25 wt. % or greater, or 40 wt. % orgreater, or 60 wt. % or greater, based on the total weight of the acidcopolymer. The acid is typically present in the acid copolymer in anamount of 6 wt. % or greater, or 9 wt. % or greater, or 10 wt. % orgreater, or 11 wt. % or greater, or 15 wt. % or greater, or 16 wt. % orgreater, or in an amount within a range having a lower limit of 1 or 4or 5 or 6 or 8 or 10 or 11 or 12 or 15 wt. % and an upper limit of 15 or16 or 17 or 19 or 20 or 20.5 or 21 or 25 or 30 or 35 or 40 wt. %, basedon the total weight of the acid copolymer. The optional softeningmonomer is typically present in the acid copolymer in an amount within arange having a lower limit of 0 or 1 or 3 or 5 or 11 or 15 or 20 wt. %and an upper limit of 23 or 25 or 30 or 35 or 50 wt. %, based on thetotal weight of the acid copolymer.

The O/X or O/X/Y-type copolymer is at least partially neutralized with acation source, optionally in the presence of a high molecular weightorganic acid, such as those disclosed in U.S. Pat. No. 6,756,436, theentire disclosure of which is hereby incorporated herein by reference.The acid copolymer can be reacted with the optional high molecularweight organic acid and the cation source simultaneously, or prior tothe addition of the cation source. Suitable cation sources include, butare not limited to, metal ion sources, such as compounds of alkalimetals, alkaline earth metals, transition metals, and rare earthelements; ammonium salts and monoamine salts; and combinations thereof.Preferred cation sources are compounds of magnesium, sodium, potassium,cesium, calcium, barium, manganese, copper, zinc, lead, tin, aluminum,nickel, chromium, lithium, and rare earth metals.

Non-limiting examples of suitable commercially available ionomers andother thermoplastic materials that can be used in accordance with thisinvention are Surlyn® ionomers and DuPont® HPF 1000 and HPF 2000 highlyneutralized polymers, commercially available from E. I. du Pont deNemours and Company; Clarix® ionomers, commercially available from A.Schulman, Inc.; Iotek® ionomers, commercially available from ExxonMobilChemical Company; and Amplify® IO ionomers, commercially available fromThe Dow Chemical Company; Amplify® GR functional polymers and Amplify®TY functional polymers, commercially available from The Dow ChemicalCompany; Fusabond® functionalized polymers, commercially available fromE. I. du Pont de Nemours and Company; Exxelor® maleic anhydride graftedpolymers, commercially available from ExxonMobil Chemical Company;ExxonMobil® PP series polypropylene impact copolymers, commerciallyavailable from ExxonMobil Chemical Company; Vistamaxx® propylene-basedelastomers, commercially available from ExxonMobil Chemical Company;Exact® plastomers, commercially available from ExxonMobil ChemicalCompany; Santoprene® thermoplastic vulcanized elastomers, commerciallyavailable from ExxonMobil Chemical Company; Kraton® styrenic blockcopolymers, commercially available from Kraton Performance PolymersInc.; Septon® styrenic block copolymers, commercially available fromKuraray Co., Ltd.; Lotader® ethylene acrylate based polymers,commercially available from Arkema Corporation; Polybond® graftedpolyethylenes and polypropylenes, commercially available from ChemturaCorporation; Pebax® polyether and polyester amides, commerciallyavailable from Arkema Inc.; polyester-based thermoplastic elastomers,such as Hytrel® polyester elastomers, commercially available from E. I.du Pont de Nemours and Company, and Riteflex® polyester elastomers,commercially available from Ticona; Estane® thermoplastic polyurethanes,commercially available from The Lubrizol Corporation; Grivory®polyamides and Grilamid® polyamides, commercially available from EMSGrivory; Zytel® polyamide resins and Elvamide® nylon multipolymerresins, commercially available from E. I. du Pont de Nemours andCompany; Elvaloy® acrylate copolymer resins, commercially available fromE. I. du Pont de Nemours and Company; Elastollan® polyurethane-basedthermoplastic elastomers, commercially available from BASF; Xylex®polycarbonate/polyester blends, commercially available from SABICInnovative Plastics; and combinations of two or more thereof.

As discussed above, the acid is typically present in the O/X orO/X/Y-type copolymer in an amount of 6 wt. % or greater. “Low acid” and“high acid” ionomeric copolymers, as well as blends of such ionomers,may be used. In general, low acid ionomers are considered to be thosecontaining 16 wt. % or less of acid moieties, whereas high acid ionomersare considered to be those containing greater than 16 wt. % of acidmoieties. The acidic groups in the acid copolymers are partially ortotally-neutralized with a cation source. Suitable cation sourcesinclude metal cations and salts thereof, organic amine compounds,ammonium, and combinations thereof. Suitable cation sources include, forexample, metal cations and salts thereof, wherein the metal ispreferably lithium, sodium, potassium, magnesium, calcium, barium, lead,tin, zinc, aluminum, manganese, nickel, chromium, copper, or acombination thereof. The metal cation salts provide the cations capableof neutralizing (at varying levels) the carboxylic acids of the ethyleneacid copolymer and fatty acids, if present, as discussed further below.These include, for example, the sulfate, carbonate, acetate, oxide, orhydroxide salts of lithium, sodium, potassium, magnesium, calcium,barium, lead, tin, zinc, aluminum, manganese, nickel, chromium, copper,or a combination thereof. Preferred metal cation salts are calcium andmagnesium-based salts. High surface area cation particles such as microand nano-scale cation particles are preferred. The amount of cation usedin the composition is readily determined based on desired level ofneutralization.

For example, olefin acid copolymer ionomer resins having acid groupsthat are neutralized from about 10 percent or greater may be used. Inone ionomer composition, the acid groups are partially-neutralized. Thatis, the neutralization level is from about 10% to about 70%, morepreferably 20% to 60%, and most preferably 30 to 50%. These ionomercompositions, containing acid groups neutralized to 70% or less, may bereferred to ionomers having relatively low neutralization levels orpartial-neutralization. On the other hand, the ionomer composition maycontain acid groups that are highly or fully-neutralized. In these HNPs,the neutralization level is greater than 70%, preferably at least 90%,and even more preferably at least 100%. In another embodiment, an excessamount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater.

When the α-olefin monomer is ethylene, such copolymers are referred toherein as E/X-type copolymers and when a softening monomer is included,such copolymers are referred to herein as E/X/Y-type copolymers, whereinE is ethylene; X is a C₃ to C₈ α,β-ethylenically unsaturated mono- ordicarboxylic acid; and Y is a softening monomer. The softening monomeris typically an alkyl (meth) acrylate, wherein the alkyl groups havefrom 1 to 8 carbon atoms. Preferred E/X/Y-type copolymers are thosewherein X is (meth) acrylic acid and/or Y is selected from (meth)acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, methyl(meth) acrylate, and ethyl (meth) acrylate. More preferred E/X/Y-typecopolymers are ethylene/(meth) acrylic acid/n-butyl acrylate,ethylene/(meth) acrylic acid/methyl acrylate, and ethylene/(meth)acrylic acid/ethyl acrylate.

The amount of ethylene in the E/X and E/X/Y-type copolymers is typicallyat least 15 wt. %, preferably at least 25 wt. %, more preferably least40 wt. %, and even more preferably at least 60 wt. %, based on totalweight of the copolymer. The amount of C₃ to C₈ α,β-ethylenicallyunsaturated mono- or dicarboxylic acid in the ethylene acid copolymer istypically from 1 wt. % to 35 wt. %, preferably from 5 wt. % to 30 wt. %,more preferably from 5 wt. % to 25 wt. %, and even more preferably from10 wt. % to 20 wt. %, based on total weight of the copolymer. The amountof optional softening monomer in the ethylene acid copolymer istypically from 0 wt. % to 50 wt. %, preferably from 5 wt. % to 40 wt. %,more preferably from 10 wt. % to 35 wt. %, and even more preferably from20 wt. % to 30 wt. %, based on total weight of the copolymer. Asdiscussed above, “low acid” and “high acid” ionomeric polymers, as wellas blends of such ionomers, may be used. In general, low acid ionomersare considered to be those containing 16 wt. % or less of acid moieties,whereas high acid ionomers are considered to be those containing greaterthan 16 wt. % of acid moieties.

As discussed above, the acidic groups in the E/X and E/X/Y-typecopolymer ionomers are partially or totally neutralized with a cationsource. Suitable cation sources include metal cations and salts thereof,organic amine compounds, ammonium, and combinations thereof. Preferredcation sources are metal cations and salts thereof, wherein the metal ispreferably lithium, sodium, potassium, magnesium, calcium, barium, lead,tin, zinc, aluminum, manganese, nickel, chromium, copper, or acombination thereof. The metal cation salts provide the cations capableof neutralizing (at varying levels) the carboxylic acids of the ethyleneacid copolymer and fatty acids, if present, as discussed further below.These include, for example, the sulfate, carbonate, acetate, oxide, orhydroxide salts of lithium, sodium, potassium, magnesium, calcium,barium, lead, tin, zinc, aluminum, manganese, nickel, chromium, copper,or a combination thereof. Preferred metal cation salts are calcium andmagnesium-based salts. High surface area cation particles such as microand nano-scale cation particles are preferred. The amount of cation usedin the composition is readily determined based on desired level ofneutralization.

For example, ethylene acid copolymers having acid groups that areneutralized from about 10 percent or greater may be used. In oneethylene acid copolymer composition, the acid groups arepartially-neutralized. That is, the neutralization level is from about10% to about 70%, more preferably 20% to 60%, and most preferably 30 to50%. These ethylene acid copolymer compositions, containing acid groupsneutralized to 70% or less, may be referred to ionomers havingrelatively low neutralization levels or partial-neutralization. On theother hand, the ethylene acid copolymer composition may contain acidgroups that are highly or fully-neutralized. In these HNPs, theneutralization level is greater than 70%, preferably at least 90%, andeven more preferably at least 100%. In another embodiment, an excessamount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater. In one preferred embodiment, a highacid ethylene acid copolymer containing about 19 to 20 wt. % methacrylicor acrylic acid is neutralized with zinc and sodium cations to a 95%neutralization level.

“Ionic plasticizers” such as organic acids or salts of organic acids,particularly fatty acids, may be added to any of the ionomer resins ifneeded. Such ionic plasticizers are used to make conventional ionomercomposition more processable as described in Rajagopalan et al., U.S.Pat. No. 6,756,436, the disclosure of which is hereby incorporated byreference. In one preferred embodiment, the thermoplastic ionomercomposition, containing acid groups neutralized to 70% or less, does notinclude a fatty acid or salt thereof, or any other ionic plasticizer. Onthe other hand, the thermoplastic ionomer composition, containing acidgroups neutralized to greater than 70%, includes an ionic plasticizer,particularly a fatty acid or salt thereof. For example, the ionicplasticizer may be added in an amount of 0.5 to 10 pph, more preferably1 to 5 pph. The organic acids may be aliphatic, mono- ormulti-functional (saturated, unsaturated, or multi-unsaturated) organicacids. Salts of these organic acids may also be employed. Suitable fattyacid salts include, for example, metal stearates, laureates, oleates,palmitates, pelargonates, and the like. For example, fatty acid saltssuch as zinc stearate, calcium stearate, magnesium stearate, bariumstearate, and the like can be used. The salts of fatty acids aregenerally fatty acids neutralized with metal ions. The metal cationsalts provide the cations capable of neutralizing (at varying levels)the carboxylic acid groups of the fatty acids. Examples include thesulfate, carbonate, acetate and hydroxide salts of metals such asbarium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper,potassium, strontium, titanium, tungsten, magnesium, cesium, iron,nickel, silver, aluminum, tin, or calcium, and blends thereof. It ispreferred the organic acids and salts be relatively non-migratory (theydo not bloom to the surface of the polymer under ambient temperatures)and non-volatile (they do not volatilize at temperatures required formelt-blending).

As noted above, the final ionomer compositions may contain additionalmaterials such as, for example, a small amount of ionic plasticizer,which is particularly effective at improving the processability ofhighly-neutralized ionomers. For example, the ionic plasticizer may beadded in an amount of 0.5 to 10 pph, more preferably 1 to 5 pph. Inaddition to the fatty acids and salts of fatty acids discussed above,other suitable ionic plasticizers include, for example, polyethyleneglycols, waxes, bis-stearamides, minerals, and phthalates. In anotherembodiment, an amine or pyridine compound is used, preferably inaddition to a metal cation. Suitable examples include, for example,ethylamine, methylamine, diethylamine, tert-butylamine, dodecylamine,and the like.

The ionomer compositions may contain a wide variety of fillers and someof these fillers may be used to adjust the specific gravity of thecomposition as needed. High surface-area fillers that have an affinityfor the acid groups in ionomer may be used. In particular, fillers suchas particulate, fibers, or flakes having cationic nature such that theymay also contribute to the neutralization of the ionomer are suitable.For example, aluminum oxide, zinc oxide, tin oxide, barium sulfate, zincsulfate, calcium oxide, calcium carbonate, zinc carbonate, bariumcarbonate, tungsten, tungsten carbide, and lead silicate fillers may beused. Also, silica, fumed silica, and precipitated silica, such as thosesold under the tradename, HISIL™, from PPG Industries, carbon black,carbon fibers, and nano-scale materials such as nanotubes, nanoflakes,nanofillers, and nanoclays may be used. Relatively heavy-weight fillersalso may be added to the ionomer compositions including, but not limitedto, particulate, powders, fibers and flakes of heavy metals such ascopper, nickel, tungsten, brass, steel, magnesium, molybdenum, cobalt,lead, tin, silver, gold, and platinum, and alloys thereof. Steelmaterials also can be added. In other instances, it may be desirable toadd relatively light-weight metals such as titanium and aluminum alloysthereof. Other additives and fillers include, but are not limited to,chemical blowing and foaming agents, optical brighteners, coloringagents, fluorescent agents, whitening agents, UV absorbers, lightstabilizers, defoaming agents, processing aids, antioxidants,stabilizers, softening agents, fragrance components, plasticizers,impact modifiers, titanium dioxide, acid copolymer wax, surfactants,rubber regrind (recycled core material), clay, mica, talc, glass flakes,milled glass, and mixtures thereof. Suitable additives are more fullydescribed in, for example, Rajagopalan et al., U.S. Patent ApplicationPublication No. 2003/0225197, the entire disclosure of which is herebyincorporated herein by reference. In a particular embodiment, the totalamount of additive(s) and filler(s) present in the final thermoplasticionomeric composition is 25 wt. % or less, or 20 wt. % or less, or 15wt. % or less, or 12 wt. % or less, or 10 wt. % or less, or 9 wt. % orless, or 6 wt. % or less, or 5 wt. % or less, or 4 wt. % or less, or 3wt. % or less, based on total weight of the ionomeric composition.

The acid copolymer ionomer is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of acid copolymer is about 40 to about 95 weight percent.

Other suitable thermoplastic polymers that may be used to form the outercore layer include, but are not limited to, the following polymers(including homopolymers, copolymers, and derivatives thereof.)

(a) polyesters, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof;

(b) polyamides, polyamide-ethers, and polyamide-esters, and thosedisclosed in U.S. Pat. Nos. 6,187,864, 6,001,930, and 5,981,654, theentire disclosures of which are hereby incorporated herein by reference,and blends of two or more thereof;

(c) polyurethanes, polyureas, polyurethane-polyurea hybrids, and blendsof two or more thereof;

(d) fluoropolymers, such as those disclosed in U.S. Pat. Nos. 5,691,066,6,747,110 and 7,009,002, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof;

(e) polystyrenes, such as poly(styrene-co-maleic anhydride),acrylonitrile-butadiene-styrene, poly(styrene sulfonate), polyethylenestyrene, and blends of two or more thereof;

(f) polyvinyl chlorides and grafted polyvinyl chlorides, and blends oftwo or more thereof;

(g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof;

(h) polyethers, such as polyarylene ethers, polyphenylene oxides, blockcopolymers of alkenyl aromatics with vinyl aromatics and polyamicesters,and blends of two or more thereof;

(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and

(j) polycarbonate/polyester copolymers and blends.

These thermoplastic polymers may be used by and in themselves to formthe outer core layer, or blends of thermoplastic polymers including theabove-described polymers and ethylene acid copolymer ionomers may beused. It also is recognized that the ionomer compositions may contain ablend of two or more ionomers. For example, the composition may containa 50/50 wt. % blend of two different highly-neutralizedethylene/methacrylic acid copolymers. In another version, thecomposition may contain a blend of one or more ionomers and a maleicanhydride-grafted non-ionomeric polymer. The non-ionomeric polymer maybe a metallocene-catalyzed polymer. In another version, the compositioncontains a blend of a highly-neutralized ethylene/methacrylic acidcopolymer and a maleic anhydride-grafted metallocene-catalyzedpolyethylene. In yet another version, the composition contains amaterial selected from the group consisting of highly-neutralizedionomers optionally blended with a maleic anhydride-graftednon-ionomeric polymer; polyester elastomers; polyamide elastomers; andcombinations of two or more thereof.

Core Structure

As discussed above, the core of the golf ball of this inventionpreferably has a dual-layered structure comprising an inner core andouter core layer. Referring to FIG. 3, one version of a golf ball thatcan be made in accordance with this invention is generally indicated at(20). The ball (20) contains a dual-layered core (22) having an innercore (center) (22 a) and outer core layer (22 b) surrounded by asingle-layered cover (24). The inner core (22 a) is relatively small involume and generally has a diameter within a range of about 0.10 toabout 1.10 inches. More particularly, the inner core (22 a) preferablyhas a diameter size with a lower limit of about 0.15 or 0.25 or 0.35 or0.45 or 0.55 inches and an upper limit of about 0.60 or 0.70 or 0.80 or0.90 inches. In one preferred version, the diameter of the inner core(22 a) is in the range of about 0.025 to about 0.080 inches, morepreferably about 0.030 to about 0.075 inches. Meanwhile, the outer corelayer (22 b) generally has a thickness within a range of about 0.010 toabout 0.250 inches and preferably has a lower limit of 0.010 or 0.020 or0.025 or 0.030 inches and an upper limit of 0.070 or 0.080 or 0.100 or0.200 inches. In one preferred version, the outer core layer has athickness in the range of about 0.040 to about 0.170 inches, morepreferably about 0.060 to about 0.150 inches.

Referring to FIG. 4, in another version, the golf ball (25) contains adual-core (26) having an inner core (center) (26 a) and outer core layer(26 b). The dual-core (26) is surrounded by a multi-layered cover (28)having an inner cover layer (28 a) and outer cover layer (28 b).

The hardness of the core sub-assembly (inner core and outer core layer)is an important property. In general, cores with relatively highhardness values have higher compression and tend to have good durabilityand resiliency. However, some high compression balls are stiff and thismay have a detrimental effect on shot control and placement. Thus, theoptimum balance of hardness in the core sub-assembly needs to beattained.

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center); and the outer core layer has a“positive” hardness gradient (that is, the outer surface of the outercore layer is harder than the inner surface of the outer core layer.) Insuch cases where both the inner core and outer core layer each has a“positive” hardness gradient, the outer surface hardness of the outercore layer is preferably greater than the hardness of the geometriccenter of the inner core. In one preferred version, the positivehardness gradient of the inner core is in the range of about 2 to about40 Shore C units and even more preferably about 10 to about 25 Shore Cunits; while the positive hardness gradient of the outer core is in therange of about 2 to about 20 Shore C and even more preferably about 3 toabout 10 Shore C.

In an alternative version, the inner core may have a positive hardnessgradient; and the outer core layer may have a “zero” hardness gradient(that is, the hardness values of the outer surface of the outer corelayer and the inner surface of the outer core layer are substantiallythe same) or a “negative” hardness gradient (that is, the outer surfaceof the outer core layer is softer than the inner surface of the outercore layer.) For example, in one version, the inner core has a positivehardness gradient; and the outer core layer has a negative hardnessgradient in the range of about 2 to about 25 Shore C. In a secondalternative version, the inner core may have a zero or negative hardnessgradient; and the outer core layer may have a positive hardnessgradient. Still yet, in another embodiment, both the inner core andouter core layers have zero or negative hardness gradients.

In general, hardness gradients are further described in Bulpett et al.,U.S. Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which arehereby incorporated by reference. Methods for measuring the hardness ofthe inner core and outer core layers along with other layers in the golfball and determining the hardness gradients of the various layers aredescribed in further detail below. The core layers have positive,negative, or zero hardness gradients defined by hardness measurementsmade at the outer surface of the inner core (or outer surface of theouter core layer) and radially inward towards the center of the innercore (or inner surface of the outer core layer). These measurements aremade typically at 2-mm increments as described in the test methodsbelow. In general, the hardness gradient is determined by subtractingthe hardness value at the innermost portion of the component beingmeasured (for example, the center of the inner core or inner surface ofthe outer core layer) from the hardness value at the outer surface ofthe component being measured (for example, the outer surface of theinner core or outer surface of the outer core layer).

Positive Hardness Gradient.

For example, if the hardness value of the outer surface of the innercore is greater than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface harder than its geometriccenter), the hardness gradient will be deemed “positive” (a largernumber minus a smaller number equals a positive number.) For example, ifthe outer surface of the inner core has a hardness of 67 Shore C and thegeometric center of the inner core has a hardness of 60 Shore C, thenthe inner core has a positive hardness gradient of 7. Likewise, if theouter surface of the outer core layer has a greater hardness value thanthe inner surface of the outer core layer, the given outer core layerwill be considered to have a positive hardness gradient.

Negative Hardness Gradient.

On the other hand, if the hardness value of the outer surface of theinner core is less than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface softer than its geometriccenter), the hardness gradient will be deemed “negative.” For example,if the outer surface of the inner core has a hardness of 68 Shore C andthe geometric center of the inner core has a hardness of 70 Shore C,then the inner core has a negative hardness gradient of 2. Likewise, ifthe outer surface of the outer core layer has a lesser hardness valuethan the inner surface of the outer core layer, the given outer corelayer will be considered to have a negative hardness gradient.

Zero Hardness Gradient.

In another example, if the hardness value of the outer surface of theinner core is substantially the same as the hardness value of the innercore's geometric center (that is, the surface of the inner core hasabout the same hardness as the geometric center), the hardness gradientwill be deemed “zero.” For example, if the outer surface of the innercore and the geometric center of the inner core each has a hardness of65 Shore C, then the inner core has a zero hardness gradient. Likewise,if the outer surface of the outer core layer has a hardness valueapproximately the same as the inner surface of the outer core layer, theouter core layer will be considered to have a zero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 3 Shore C or greater, preferably 7Shore C or greater, more preferably 10 Shore C, and even more preferably20 Shore C or greater. The term, “zero hardness gradient” as used hereinmeans a hardness gradient of less than 3 Shore C, preferably less than 1Shore C and may have a value of zero or negative 1 to negative 10 ShoreC. The term, “negative hardness gradient” as used herein means ahardness value of less than zero, for example, negative 3, negative 5,negative 7, negative 10, negative 15, or negative 20 or negative 25. Theterms, “zero hardness gradient” and “negative hardness gradient” may beused herein interchangeably to refer to hardness gradients of negative 1to negative 10.

The inner core preferably has a geometric center hardness(H_(inner core center)) of about 5 Shore D or greater. For example, the(H_(inner core center)) may be in the range of about 5 to about 88 ShoreD and more particularly within a range having a lower limit of about 5or 10 or 14 or 18 or 20 or 26 or 30 or 34 or 36 or 38 or 42 or 48 of 50or 52 Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62 or64 or 68 or 70 or 74 or 76 or 80 or 82 or 84 or 88 Shore D. In anotherexample, the center hardness of the inner core (H_(inner core center)),as measured in Shore C units, is preferably about 10 Shore C or greater;for example, the H_(inner core center) may have a lower limit of about10 or 12 or 14 or 16 or 22 or 24 or 28 or 31 or 34 or 37 or 40 or 44 or52 or 58 Shore C and an upper limit of about or 60 or 62 or 65 or 68 or71 or 74 or 76 or 78 or 79 or 80 or 84 or 90 Shore C. Concerning theouter surface hardness of the inner core (H_(inner core surface)), thishardness is preferably about 15 Shore D or greater; for example, theH_(inner core surface) may fall within a range having a lower limit ofabout 15 or 18 or 20 or 23 or 26 or 30 or 34 or 36 or 38 or 42 or 48 of50 or 52 Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62or 70 or 72 or 75 or 78 or 80 or 82 or 84 or 86 or 90 Shore D. In oneversion, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C units, has a lowerlimit of about 20 or 24 or 27 or 28 or 30 or 32 or 34 or 38 or 44 or 52or 58 or 60 or 70 or 74 Shore C and an upper limit of about 76 or 78 or80 or 84 or 86 or 88 or 90 or 92 Shore C. In another version, thegeometric center hardness (H_(inner core center)) is in the range ofabout 10 Shore C to about 50 Shore C; and the outer surface hardness ofthe inner core (H_(inner core surface)) is in the range of about 5 ShoreC to about 48 Shore C.

On the other hand, the outer core layer preferably has an outer surfacehardness (H_(outer surface of OC)) of about 40 Shore D or greater, andmore preferably within a range having a lower limit of about 40 or 42 or44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90Shore D. The outer surface hardness of the outer core layer(H_(outer surface of OC)), as measured in Shore C units, preferably hasa lower limit of about 40 or 42 or 43 or 45 or 48 or 50 or 54 or 58 or60 or 63 or 65 or 67 or 70 or 73 or 76 Shore C, and an upper limit ofabout 78 or 80 or 84 or 85 or 87 or 89 or 90 or 92 or 95 Shore C. And,the inner surface of the outer core layer (H_(inner surface of OC))preferably has a hardness of about 40 Shore D or greater, and morepreferably within a range having a lower limit of about 40 or 42 or 44or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or 60or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90 ShoreD. The inner surface hardness of the outer core layer(H_(inner surface of OC)), as measured in Shore C units, preferably hasa lower limit of about 40 or 44 or 45 or 47 or 50 or 52 or 54 or 55 or58 or 60 or 63 or 65 or 67 or 70 or 73 or 76 Shore C, and an upper limitof about 78 or 80 or 85 or 87 or 89 or 90 or 92 or 95 Shore C.

In one embodiment, the outer surface hardness of the outer core layer(H_(outer surface of OC)), is less than the outer surface hardness(H_(inner core surface)) of the inner core by at least 3 Shore C unitsand more preferably by at least 5 Shore C.

In a second embodiment, the outer surface hardness of the outer corelayer (H_(outer surface of OC)), is greater than the outer surfacehardness (H_(inner core surface)) of the inner core by at least 3 ShoreC units and more preferably by at least 5 Shore C.

The core structure also has a hardness gradient across the entire coreassembly. In one embodiment, the (H_(inner core center)) is in the rangeof about 10 Shore C to about 60 Shore C, preferably about 20 Shore C toabout 50 Shore C; and the (H_(outer surface of OC)) is in the range ofabout 40 Shore C to about 90 Shore C, preferably about 43 Shore C toabout 87 Shore C, to provide a positive hardness gradient across thecore assembly.

As discussed above, the inner core is preferably formed from a foamedthermoplastic or thermoset composition and more preferably foamedpolyurethanes. And, the outer core layer is formed preferably from anon-foamed thermoplastic composition such as ethylene acid copolymer.

The inner core preferably has a diameter in the range of about 0.100 toabout 1.100 inches. For example, the inner core may have a diameterwithin a range of about 0.100 to about 0.500 inches. In another example,the inner core may have a diameter within a range of about 0.300 toabout 0.800 inches. More particularly, the inner core may have adiameter size with a lower limit of about 0.10 or 0.12 or 0.15 or 0.25or 0.30 or 0.35 or 0.45 or 0.55 inches and an upper limit of about 0.60or 0.65 or 0.70 or 0.80 or 0.90 or 1.00 or 1.10 inches. As far as theouter core layer is concerned, it preferably has a thickness in therange of about 0.100 to about 0.750 inches. For example, the lower limitof thickness may be about 0.050 or 0.100 or 0.150 or 0.200 or 0.250 or0.300 or 0.340 or 0.400 and the upper limit may be about 0.500 or 0.550or 0.600 or 0.650 or 0.700 or 0.750 inches.

Dual-layered core structures containing layers with various thicknessand volume levels may be made in accordance with this invention. Forexample, in one version, the total diameter of the core structure is0.20 inches and the total volume of the core structure is 0.23 cc. Moreparticularly, in this example, the diameter of the inner core is 0.10inches and the volume of the inner core is 0.10 cc; while the thicknessof the outer core is 0.100 inches and the volume of the outer core is0.13 cc. In another version, the total core diameter is about 1.55inches and the total core volume is 31.96 cc. In this version, the outercore layer has a thickness of 0.400 inches and volume of 28.34 cc.Meanwhile, the inner core has a diameter of 0.75 inches and volume of3.62 cm. In one embodiment, the volume of the outer core layer isgreater than the volume of the inner core. In another embodiment, thevolume of the outer core layer and inner core are equivalent. In stillanother embodiment, the volume of the outer core layer is less than thevolume of the inner core. Other examples of core structures containinglayers of varying thicknesses and volumes are described below in Table1.

TABLE 1 Sample Core Dimensions Total Foamed Volume Core TotalThermoplastic Outer Inner of Exam- Diam- Core Outer Core Core Core Innerple eter Volume Thickness Volume Diameter Core A 0.30″  0.23 cc 0.100″ 0.13 cc 0.10″  0.10 cc B 1.60″ 33.15 cc 0.750″ 33.05 cc 0.10″  0.10 ccC 1.55″ 31.96 cc 0.225″ 11.42 cc 1.10″ 11.42 cc D 1.55″ 31.96 cc 0.400″28.34 cc 0.75″  3.62 cc E 1.55″ 31.96 cc 0.525″ 28.34 cc 0.50″  3.62 cc

In one preferred embodiment, the inner core has a specific gravity inthe range of about 0.25 to about 1.25 g/cc. Also, as discussed above,the specific gravity of the inner core may vary at different points ofthe inner core structure. That is, there may be a specific gravitygradient in the inner core. For example, in one preferred version, thegeometric center of the inner core has a density in the range of about0.25 to about 0.75 g/cc; while the outer skin of the inner core has adensity in the range of about 0.75 to about 1.50 g/cc.

Meanwhile, the outer core layer preferably has a relatively highspecific gravity. Thus, the specific gravity of the inner core layer(SG_(inner)) is preferably less than the specific gravity of the outercore layer (SG_(outer)). By the term, “specific gravity of the outercore layer” (“SG_(outer)”), it is generally meant the specific gravityof the outer core layer as measured at any point of the outer corelayer. The specific gravity values at different points in the outer corelayer may vary. That is, there may be specific gravity gradients in theouter core layer similar to the inner core. For example, the outer corelayer may have a specific gravity within a range having a lower limit ofabout 0.50 or 0.60 or 0.70 or 0.75 or 0.85 or 0.90 or 0.95 or 1.00 or1.10 or 1.25 or 1.30 or 1.36 or 1.40 or 1.42 or 1.48 or 1.50 or 1.60 or1.66 or 1.75 or 2.00 and an upper limit of 2.50 or 2.60 or 2.80 or 2.90or 3.00 or 3.10 or 3.25 or 3.50 or 3.60 or 3.80 or 4.00, 4.25 or 5.00 or5.10 or 5.20 or 5.30 or 5.40 or 6.00 or 6.20 or 6.25 or 6.30 or 6.40 or6.50 or 7.00 or 7.10 or 7.25 or 7.50 or 7.60 or 7.65 or 7.80 or 8.00 or8.20 or 8.50 or 9.00 or 9.75 or 10.00 g/cc.

In general, the specific gravities of the respective pieces of an objectaffect the Moment of Inertia (MOI) of the object. The Moment of Inertiaof a ball (or other object) about a given axis generally refers to howdifficult it is to change the ball's angular motion about that axis. Ifthe ball's mass is concentrated towards the center (the center piece(for example, inner core) has a higher specific gravity than the outerpiece (for example, outer core layers), less force is required to changeits rotational rate, and the ball has a relatively low Moment ofInertia. In such balls, most of the mass is located close to the ball'saxis of rotation and less force is needed to generate spin. Thus, theball has a generally high spin rate as the ball leaves the club's faceafter making impact. Conversely, if the ball's mass is concentratedtowards the outer surface (the outer piece (for example, outer corelayers) has a higher specific gravity than the center piece (forexample, inner core), more force is required to change its rotationalrate, and the ball has a relatively high Moment of Inertia. That is, insuch balls, most of the mass is located away from the ball's axis ofrotation and more force is needed to generate spin. Such balls have agenerally low spin rate as the ball leaves the club's face after makingimpact.

More particularly, as described in Sullivan, U.S. Pat. No. 6,494,795 andLadd et al., U.S. Pat. No. 7,651,415, the formula for the Moment ofInertia for a sphere through any diameter is given in the CRC StandardMathematical Tables, 24th Edition, 1976 at 20 (hereinafter CRCreference). The term, “specific gravity” as used herein, has itsordinary and customary meaning, that is, the ratio of the density of asubstance to the density of water at 4° C., and the density of water atthis temperature is 1 g/cm³.

In one embodiment, the golf balls of this invention are relatively lowspin and long distance. That is, the foam core construction, asdescribed above, wherein the inner core is made of a foamed compositionhelps provide a relatively low spin ball having good resiliency. Theinner foam cores of this invention preferably have a Coefficient ofRestitution (COR) of about 0.300 or greater; more preferably about 0.400or greater, and even more preferably about 0.450 or greater. Theresulting balls containing the dual-layered core constructions of thisinvention and cover of at least one layer preferably have a COR of about0.700 or greater, more preferably about 0.730 or greater; and even morepreferably about 0.750 to 0.810 or greater. The inner foam corespreferably have a Soft Center Deflection Index (“SCDI”) compression, asdescribed in the Test Methods below, in the range of about 50 to about190, and more preferably in the range of about 60 to about 170.

The USGA has established a maximum weight of 45.93 g (1.62 ounces) forgolf balls. For play outside of USGA rules, the golf balls can beheavier. In one preferred embodiment, the weight of the multi-layeredcore is in the range of about 28 to about 38 grams. Also, golf ballsmade in accordance with this invention can be of any size, although theUSGA requires that golf balls used in competition have a diameter of atleast 1.68 inches. For play outside of United States Golf Association(USGA) rules, the golf balls can be of a smaller size. Normally, golfballs are manufactured in accordance with USGA requirements and have adiameter in the range of about 1.68 to about 1.80 inches. As discussedfurther below, the golf ball contains a cover which may be multi-layeredand in addition may contain intermediate (casing) layers, and thethickness levels of these layers also must be considered. Thus, ingeneral, the dual-layer core structure normally has an overall diameterwithin a range having a lower limit of about 1.00 or 1.20 or 1.30 or1.40 inches and an upper limit of about 1.58 or 1.60 or 1.62 or 1.66inches, and more preferably in the range of about 1.3 to 1.65 inches. Inone embodiment, the diameter of the core sub-assembly is in the range ofabout 1.45 to about 1.62 inches.

Cover Structure

The golf ball sub-assemblies of this invention may be enclosed with oneor more cover layers. The golf ball sub-assembly may comprise themulti-layered core structure as discussed above. In other versions, thegolf ball sub-assembly includes the core structure and one or morecasing (mantle) layers disposed about the core. In one particularlypreferred version, the golf ball includes a multi-layered covercomprising inner and outer cover layers. The inner cover layer ispreferably formed from a composition comprising an ionomer or a blend oftwo or more ionomers that helps impart hardness to the ball. In aparticular embodiment, the inner cover layer is formed from acomposition comprising a high acid ionomer. A particularly suitable highacid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is a copolymer ofethylene and methacrylic acid, having an acid content of 19 wt %, whichis 45% neutralized with sodium. In another particular embodiment, theinner cover layer is formed from a composition comprising a high acidionomer and a maleic anhydride-grafted non-ionomeric polymer. Aparticularly suitable maleic anhydride-grafted polymer is Fusabond 525D®(DuPont). Fusabond 525D® is a maleic anhydride-grafted,metallocene-catalyzed ethylene-butene copolymer having about 0.9 wt %maleic anhydride grafted onto the copolymer. A particularly preferredblend of high acid ionomer and maleic anhydride-grafted polymer is an 84wt %/16 wt % blend of Surlyn 8150® and Fusabond 525D®. Blends of highacid ionomers with maleic anhydride-grafted polymers are furtherdisclosed, for example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, theentire disclosures of which are hereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

A wide variety of materials may be used for forming the outer coverincluding, for example, polyurethanes; polyureas; copolymers, blends andhybrids of polyurethane and polyurea; olefin-based copolymer ionomerresins (for example, Surlyn® ionomer resins and DuPont HPF® 1000 andHPF® 2000, commercially available from DuPont; Iotek® ionomers,commercially available from ExxonMobil Chemical Company; Amplify® IOionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The compositions used to make the casing (mantle) and cover layers maycontain a wide variety of fillers and additives to impart specificproperties to the ball. For example, relatively heavy-weight andlight-weight metal fillers such as, particulate; powders; flakes; andfibers of copper, steel, brass, tungsten, titanium, aluminum, magnesium,molybdenum, cobalt, nickel, iron, lead, tin, zinc, barium, bismuth,bronze, silver, gold, and platinum, and alloys and combinations thereofmay be used to adjust the specific gravity of the ball. Other additivesand fillers include, but are not limited to, optical brighteners,coloring agents, fluorescent agents, whitening agents, UV absorbers,light stabilizers, surfactants, processing aids, antioxidants,stabilizers, softening agents, fragrance components, plasticizers,impact modifiers, titanium dioxide, clay, mica, talc, glass flakes,milled glass, and mixtures thereof.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 75 or 80 or 82 Shore C and an upper limitof 85 or 86 or 90 or 92 Shore C. The thickness of the casing layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or0.120 inches. The outer cover layer preferably has a material hardnessof 85 Shore C or less. The thickness of the outer cover layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080inches. Methods for measuring hardness of the layers in the golf ballare described in further detail below.

A single cover or, preferably, an inner cover layer is formed around theouter core layer. When an inner cover layer is present, an outer coverlayer is formed over the inner cover layer. Most preferably, the innercover is formed from an ionomeric material and the outer cover layer isformed from a polyurethane material, and the outer cover layer has ahardness that is less than that of the inner cover layer. Preferably,the inner cover has a hardness of greater than about 60 Shore D and theouter cover layer has a hardness of less than about 60 Shore D. In analternative embodiment, the inner cover layer is comprised of apartially or fully neutralized ionomer, a thermoplastic polyesterelastomer such as Hytrel™, commercially available form DuPont, athermoplastic polyether block amide, such as Pebax™, commerciallyavailable from Arkema, Inc., or a thermoplastic or thermosettingpolyurethane or polyurea, and the outer cover layer is comprised of anionomeric material. In this alternative embodiment, the inner coverlayer has a hardness of less than about 60 Shore D and the outer coverlayer has a hardness of greater than about 55 Shore D and the innercover layer hardness is less than the outer cover layer hardness.

As discussed above, the core structure of this invention may be enclosedwith one or more cover layers. In one embodiment, a multi-layered covercomprising inner and outer cover layers is formed, where the inner coverlayer has a thickness of about 0.01 inches to about 0.06 inches, morepreferably about 0.015 inches to about 0.040 inches, and most preferablyabout 0.02 inches to about 0.035 inches. In this version, the innercover layer is formed from a partially- or fully-neutralized ionomerhaving a Shore D hardness of greater than about 55, more preferablygreater than about 60, and most preferably greater than about 65. Theouter cover layer, in this embodiment, preferably has a thickness ofabout 0.015 inches to about 0.055 inches, more preferably about 0.02inches to about 0.04 inches, and most preferably about 0.025 inches toabout 0.035 inches, with a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. The innercover layer is harder than the outer cover layer in this version. Apreferred outer cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer, blend, or hybrid thereof having aShore D hardness of about 40 to about 50. In another multi-layer cover,dual-core embodiment, the outer cover and inner cover layer materialsand thickness are the same but, the hardness range is reversed, that is,the outer cover layer is harder than the inner cover layer. For thisharder outer cover/softer inner cover embodiment, the ionomer resinsdescribed above would preferably be used as outer cover material.

Manufacturing of Golf Balls

As described above, the inner core preferably is formed by a castingmethod. The outer core layer, which surrounds the inner core, is formedby molding compositions over the inner core. Compression or injectionmolding techniques may be used to form the other layers of the coresub-assembly. Then, the casing and/or cover layers are applied over thecore sub-assembly. Prior to this step, the core structure may besurface-treated to increase the adhesion between its outer surface andthe next layer that will be applied over the core. Suchsurface-treatment may include mechanically or chemically-abrading theouter surface of the core. For example, the core may be subjected tocorona-discharge, plasma-treatment, silane-dipping, or other treatmentmethods known to those in the art.

The cover layers are formed over the core or ball sub-assembly (the corestructure and any casing layers disposed about the core) using asuitable technique such as, for example, compression-molding,flip-molding, injection-molding, retractable pin injection-molding,reaction injection-molding (RIM), liquid injection-molding, casting,spraying, powder-coating, vacuum-forming, flow-coating, dipping,spin-coating, and the like. Preferably, each cover layer is separatelyformed over the ball subassembly. For example, an ethylene acidcopolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the core sub-assembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the sub-assembly.In another method, the ionomer composition is injection-molded directlyonto the core sub-assembly using retractable pin injection molding. Anouter cover layer comprising a polyurethane or polyurea composition overthe ball sub-assembly may be formed by using a casting process.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball.

Different ball constructions can be made using the core construction ofthis invention as shown in FIGS. 1-4 discussed above. Such golf ballconstructions include, for example, five-piece, and six-piececonstructions. It should be understood that the golf balls shown inFIGS. 1-4 are for illustrative purposes only, and they are not meant tobe restrictive. Other golf ball constructions can be made in accordancewith this invention.

For example, other constructions include a core sub-assembly having afoam or non-foam inner core (center); and a foam or non-foam outer corelayer. Dual-core sub-assemblies (inner core and outer core layer),wherein the inner core and/or the outer core layer is foamed also may bemade. Furthermore, the inner cover layer, which surrounds the coresub-assembly, may be foamed or non-foamed. As discussed above,thermoplastic and thermoset foam compositions may be used to form thedifferent layers. Where more than one foam layer is used in a singlegolf ball, the foamed composition may be the same or different, and thecomposition may have the same or different hardness or specific gravityvalues. For example, a golf ball may contain a dual-core having a foamedcenter with a specific gravity of about 0.40 g/cc and a geometric centerhardness of about 50 Shore C and a center surface hardness of about 75Shore C that is formed from a polyurethane composition and an outer corelayer that is formed from a foamed highly neutralized ionomercomposition, wherein the outer core layer has a specific gravity ofabout 0.80 g/cc and a surface hardness of about 80 Shore C.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dhardness) was measured according to the test method ASTM D-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Drop Rebound.

By “drop rebound,” it is meant the number of inches a sphere willrebound when dropped from a height of 72 inches in this case, measuringfrom the bottom of the sphere. A scale, in inches is mounted directlybehind the path of the dropped sphere and the sphere is dropped onto aheavy, hard base such as a slab of marble or granite (typically about 1ft wide by 1 ft high by 1 ft deep). The test is carried out at about72-75° F. and about 50% RH

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball sub-assembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

The present invention is illustrated further by the following Examples,but these Examples should not be construed as limiting the scope of theinvention.

EXAMPLES

In the following Examples, different foam formulations were used toprepare core samples using the above-described molding methods. Thedifferent formulations are described in Tables 2 and 3 below.

TABLE 2 (Sample A) Ingredient Weight Percent 4,4 Methylene DiphenylDiisocyanate (MDI) 14.65% Polyetratmethylene ether glycol (PTMEG 34.92%2000) *Mondur ™ 582 (2.5 fn) 29.11% Trifunctional caprolactone polyol(CAPA 20.22% 3031) (3.0 fn) Water 0.67% **Niax ™ L-1500 surfactant 0.04%***KKAT ™ XK 614 catalyst 0.40% Dibutyl tin dilaurate (T-12) 0.03%*Mondur ™ 582 (2.5 fn) - polymeric methylene diphenyl diisocyanate(p-MDI) with 2.5 functionality, available from Bayer Material Science.**Niax ™ L-1500 silicone-based surfactant, available from MomentiveSpecialty Chemicals, Inc. ***KKAT ™ XK 614 zinc-based catalyst,available from King Industries.The formulation described in above Table 2 was used to make a coresample (Sample A) and the sample was evaluated and tested. The sphericalcore Sample A (0.75 inch diameter) had a density of 0.45 g/cm³, acompression (SCDI) of 75, and drop rebound of 46% based on averagemeasurements using the test methods as described above.

TABLE 3 (Sample B) Ingredient Weight Percent Mondur ™ 582 (2.5 fn)30.35% *Desmodur ™ 3900 aliphatic 30.35% **Polymeg ™ 650 19.43%***Ethacure ™ 300 19.43% Water 0.31% Niax ™ L-1500 surfactant 0.04%Dibutyl tin dilaurate (T-12) 0.09% *Desmodur ™ 3900 - polyfunctionalaliphatic polyisocyanate resin based on hexamethylene diisocyanate(HDI), available from Bayer Material Science. **Polymeg ™ 650 -polyetratmethylene ether glycol, available from Lyondell ChemicalCompany. ***Ethacure ™ 300 - aromatic diamine curing agent, availablefrom Albemarle Corp.The formulation described in above Table 3 was used to make a coresample (Sample B) and the sample was evaluated and tested. The resultingspherical core Sample B (0.75 inch diameter) had a density of 0.61g/cm³, a compression (SCDI) of 160, and drop rebound of 56% based onaverage measurements using the test methods as described above.

Prophetic Examples

The following prophetic examples describe two-layered core structuresthat may be made in accordance with this invention. The foam center ofthe core may be made using a polyurethane foam formulation as describedabove in Tables 2 and 3 or any other suitable foam material as describeabove. The outer core layer may be made of an ethylene acid copolymerionomer or any other suitable thermoplastic material as described above.

Example 1

Two-layered core (foam center and thermoplastic outer layer) having acenter diameter of 0.5 inches and a hardness gradient across the core(as measured at points in millimeters (mm) from the geometric center) inthe range of about 41 Shore C to about 81 Shore C. The hardness plot ofthis core structure is shown in FIG. 5A.

Example 2

Two-layered core (foam center and thermoplastic outer layer) having acenter diameter of 0.5 inches and a hardness gradient across the core(as measured at mm points from the geometric center) in the range ofabout 26 Shore C to about 74 Shore C. The hardness plot of this corestructure is shown in FIG. 5B.

Example 3

Two-layered core (foam center and thermoplastic outer layer) having acenter diameter of 0.5 inches and a hardness gradient across the core(as measured at mm points from the geometric center) in the range ofabout 51 Shore C to about 73 Shore C. The hardness plot of this corestructure is shown in FIG. 5C.

Example 4

Two-layered core (foam center and thermoplastic outer layer) having acenter diameter of 0.75 inches and a hardness gradient across the core(as measured at mm points from the geometric center) in the range ofabout 24 Shore C to about 82 Shore C. The hardness plot of this corestructure is shown in FIG. 5D.

It is understood that the golf ball compositions, materials, structures,products, and examples described and illustrated herein represent onlysome embodiments of the invention. It is appreciated by those skilled inthe art that various changes and additions can be made to compositions,materials, structures, products, and examples without departing from thespirit and scope of this invention. It is intended that all suchembodiments be covered by the appended claims.

When numerical lower limits and numerical upper limits are set forthherein, it is contemplated that any combination of these values may beused. Other than in the operating examples, or unless otherwiseexpressly specified, all of the numerical ranges, amounts, values andpercentages such as those for amounts of materials and others in thespecification may be read as if prefaced by the word “about” even thoughthe term “about” may not expressly appear with the value, amount orrange. Accordingly, unless indicated to the contrary, the numericalparameters set forth in the specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the present invention.

All patents, publications, test procedures, and other references citedherein, including priority documents, are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted.

We claim:
 1. A golf ball comprising: i) an inner core layer comprising afoamed composition, the inner core layer having a diameter in the rangeof about 0.100 to about 1.100 inches, a specific gravity (SG_(inner)),and an outer surface hardness (H_(inner core surface)) and a centerhardness (H_(inner core center)), the H_(inner core surface) being thesame or less than the H_(inner core center) to provide a zero ornegative hardness gradient; and ii) an outer core layer comprising athermoplastic material, the outer core layer being disposed about theinner core and having a thickness in the range of about 0.100 to about0.750 inches, a specific gravity (SG_(outer)), and an outer surfacehardness (H_(outer surface of OC)) and an inner surface hardness(H_(inner surface of OC)), the H_(outer surface of OC) being the same orless than the H_(inner surface of OC) to provide a zero or negativehardness gradient, wherein the SG_(outer), is greater than theSG_(inner), wherein the thermoplastic material is a highly-neutralizedionomer composition comprising an E/X/Y-type copolymer, wherein E isethylene, X is a C₃-C₈ α,β-ethylenically unsaturated carboxylic acidpresent in an amount of 10 to 20 wt. %, based on total weight of thecopolymer, and Y is an acrylate selected from alkyl acrylates and arylacrylates present in an amount of 0 to 50 wt. %, based on total weightof the copolymer, wherein greater than 70% of the acid groups present inthe composition are neutralized with a metal ion.
 2. The golf ball ofclaim 1, wherein the inner core comprises a foamed polyurethanecomposition.
 3. The golf ball of claim 1, wherein theH_(inner core center) is in the range of about 12 Shore C to about 50Shore C and the H_(outer surface of OC) is in the range of about 5 ShoreC to about 48 Shore C.
 4. The golf ball of claim 1, wherein theH_(inner surface of OC) is in the range of about 46 Shore C to about 86Shore C and the H_(outer surface of OC) is in the range of about 40Shore C to about 80 Shore C.
 5. The golf ball of claim 4, wherein theH_(inner surface of OC) is in the range of about 58 Shore C to about 78Shore C and the H_(outer surface of OC) is in the range of about 50Shore C to about 70 Shore C.
 6. The golf ball of claim 1, wherein theH_(inner core center) is in the range of about 12 Shore C to about 48Shore C and the H_(outer surface of OC) is in the range of about 40Shore C to about 80 Shore C to provide a positive hardness gradientacross the core assembly.